(i) Field of the Invention
The present invention relates to a head for supplying a cryogenic liquid, which head is intended to be mounted on the end of a transfer line fed by a source of said liquid, said line comprising a downstream outlet orifice for said liquid.
(ii) Description of Related Art
Such transfer lines find applications in various fields of the art, particularly the food and pharmaceutical spheres, where it is necessary to deliver doses of cryogenic liquid, at a fairly high rate, and either continuously or discontinuously.
These lines are used, in particular, in order to deliver liquid nitrogen to containers containing foodstuffs, just before these containers are sealed. The purpose of this operation is, on the one hand, to pressurize, and therefore rigidify, the container, using the vaporization of the nitrogen which causes the container to inflate. This operation also allows the foodstuffs to be inerted by reducing the residual oxygen content and therefore allows the shelf life to be extended.
This operation of supplying cryogenic liquid is, however, particularly tricky and must be performed with extreme precision. This is because it is necessary for each container to receive the same, and most precise possible, amount of liquid so that the internal pressure will not vary from one container to another. If too little liquid is delivered to the containers, then these containers will deform during handling, and in particular, when stacked. By contrast, if they receive too much liquid, they will deform or even explode because the pressure they have inside them is then excessive.
The precision required for this operation of supplying cryogenic liquid is particularly difficult to achieve. In effect, the containers travel on a conveyor, usually at a very high and sometimes varying rate, which may be as much as several tens of containers per second.
An additional difficulty with this operation lies in the partial vaporization of the cryogenic liquid dispensed, which means that this liquid does not flow in a vertical and continuous jet as might be desired. Furthermore, this vaporization may lead to the formation of plugs of gas which cause the retention of cryogenic liquid, and thus discontinuous flow thereof.